In order to understand the changes of the long-term firing pattern of neurons, slowly occurring changes of ionic mechanisms, particularly the slow changes of Na- and K- permeability will be investigated on crab and mammalian nerve fibers. The other objective is to understand the ways in which the muscular contraction is controlled by changes in the electrical potential of the surface membrane. An attempt will be made to investigate physiological functions of the transverse tubular system (T-system) of amphibian muscles. One problem is to investigate the passive electrical properties of the T-system. The other is to determine whether the T- system is excitable. The mechanisms by which the electrical signal of the T-system evokes the Ca-release from the sarcoplasmic reticulum will be investigated. Methodologically we will use: 1) microelectrophysiological technique, (sucrose gap), 2) skinned fiber technique, 3) microscopic cinematography, and 4) murexide dye and spectrophotometry.